1. Field of the Invention
The present invention relates to a stator for an alternator driven by an internal combustion engine, for example, and in particular, relates to the construction of neutral-point lead terminals in a stator winding of a three-phase alternator.
2. Description of the Related Art
FIG. 9 is a cross section showing a conventional alternator.
In FIG. 9, the alternator is provided with: a case 3 constructed from an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 rotatably mounted inside the case 3, a pulley 4 being fastened to a first end of the shaft 6; a Lundell-type rotor 7 fastened to the shaft 6; fans 5 fastened to both axial ends of the rotor 7; a stator 8 fastened to an inner wall of the case 3 so as to cover an outer circumferential side of the rotor 7; slip rings 9 fastened to a second end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 which slide in contact with the slip rings 9; a brush holder 11 for holding the brushes 10; a rectifier 12 which is electrically connected to the stator 8 to convert alternating current generated in a stator winding 16 of the stator 8 into direct current; a heat sink 17 fitted onto the brush holder 11; and a regulator 18 mounted on the heat sink 17 for adjusting the output voltage generated in the stator 8.
The rotor 7 is composed of a rotor winding 13 for generating magnetic flux on passage of electric current, and a pair of pole cores 20 and 21 disposed so as to cover the rotor winding 13, magnetic poles being formed in the pole cores 20 and 21 by magnetic flux generated in the rotor winding 13. The pair of pole cores 20 and 21 are made of iron, each has a number of claw-shaped magnetic poles 22 and 23 disposed on an outer circumferential perimeter at even pitch in a circumferential direction so as to project axially, and the pole cores 20 and 21 are fastened to the shaft 6 facing each other such that the claw-shaped magnetic poles 22 and 23 intermesh.
The stator 8 is provided with a stator core 15, and a stator coil 16 which generates alternating current due to changes in magnetic flux produced by the rotor winding 13 accompanying the rotation of rotor 7 wound to the stator core 15.
In the automotive alternator constructed in this manner, electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor winding 13, generating magnetic flux. The claw-shaped magnetic poles 22 of the pole core 20 are magnetized with north-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 23 of the pole core 21 are magnetized with south-seeking (S) poles. At the same time, rotational torque from the engine is transmitted through the belt and the pulley 4 to the shaft 6, rotating the rotor 7. Thus, a rotating magnetic field is applied to the stator winding 16, generating electromotive force in the stator coil 16. This alternating electromotive force passes through the rectifier 12 and is converted into direct current, the output thereof being adjusted by the regulator 18, and the battery being recharged.
The stator winding 16 of the stator 8 is generally a three-phase star connection, and the construction of the neutral-point connections therein is as shown in Japanese Patent Publication No. HEI 7-32555, for example.
In other words, as shown in FIG. 10, three winding phase portions are formed by winding strands of wire 24 into the stator core 15 for a required number of turns, the strands of wire 24 being composed of conducting wires having a circular cross section, and neutral-point terminals 25 of the three winding phase portions are led out from a coil end group, the three led-out neutral-point terminals 25 being brought together in one place and connected together by twisting. Then, as shown in FIG. 11, the three twisted neutral-point terminals 25 are fastened and integrated by soldering to form a neutral-point joint portion 27 which is a joint portion joining the three neutral-point terminals 25. In addition, although not shown, a neutral-point lead portion is disposed on the neutral-point joint portion 27.
Then, the neutral-point lead portion extending outwards from the neutral-point joint portion 27 extends outwards from the stator core 15 together with output terminals (output wires) 29 of each of the winding phase portions, and the neutral-point lead portion and the output terminals 29 are fastened by means of crimping to a terminal on a circuit board 12a in the rectifier 12 and are electrically connected by soldering, respectively. Thus, an alternator is provided in which output can be increased when the alternator is rotating at high speed by adding neutral-point voltage to the direct current output.
The neutral-point joint portion 27 is fastened and integrated by soldering the three neutral-point terminals 25, but in cases where the stator winding is constituted by two sets of the three winding phase portions, the neutral-point joint portion may be constructed by bringing six neutral-point terminals together in one place, connecting them by twisting them together, and fastening and integrating them by soldering.
It is desirable that the neutral-point lead portion and the output wires 29 extend outwards from the stator core 15 parallel to the axial direction to facilitate connection to the circuit board 12a. 
Furthermore, because the neutral-point terminals 25 are led around, brought together in one place and soldered, there are cases when excessive leading around of the neutral-point terminals 25 occurs due to the relative positions of the slots in which the neutral-point terminals 25 are housed. Because the long lead-around of the neutral-point terminals 25 gives rise to problems such as bringing about an increase in the amount of conducting wire, which is a heat-generating body, in other words, an increase in the amount of heat generated and an increase in electrical resistance, reducing power-generating efficiency, or giving rise to breakage of the winding and interference with other parts due to vibration when the alternator is mounted to a vehicle, it is desirable to make the lead-around of the neutral-point terminals 25 as short as possible.
In order to suppress vibration of the neutral-point joint portions 27 and the neutral-point lead portions in the presence of vibration when the alternator is mounted to the vehicle, measures have been taken to secure the lead-around portions of the neutral-point terminals 25 by binding them to the coil ends using tie-shaped bodies passing through coil end apex portions, or applying varnish to fix them to the coil ends. However, when the lead-around portions are secured to the coil ends using tie-shaped bodies, the tie-shaped bodies must be passed between the narrow spaces between the strands of wire on the coil end apex portions, decreasing work efficiency, and when the lead-around portions are secured to the coil ends by applying varnish, it is difficult to obtain a sufficient degree of securing strength with a low-viscosity varnish because the lead-around portions and the coil ends are separated by a predetermined spacing, and improvements have been called for.
In the neutral-point joint portions 27 in a stator winding 16 constructed in this manner, because a number of neutral-point terminals 25 are gathered together in one place and twisted together into a bundle then fastened and integrated by soldering, the solder 26 cannot enter between the twisted neutral-point terminals 25, and a cavity A is formed in a central portion, as shown in FIG. 12, and one problem has been that sufficient joint strength cannot be achieved, making it difficult to ensure reliability.
Because a number of neutral-point terminals 25 are soldered together, another problem has been that a high capacity jig is needed and it is necessary to heat the joint portions sufficiently, making the soldering process time-consuming and costly.
Because a number of neutral-point terminals 25 are gathered together and twisted, yet another problem has been that workability is poor.
In order to eliminate the intricate operation of gathering and twisting a number of neutral-point terminals 25 by hand, an improvement has been proposed in which the neutral-point joint portion is constructed by aligning a number of neutral-point terminals such that end surfaces thereof are positioned in the same plane and soldering these end surfaces together. However, in that proposal, the soldered surface is reduced, making the joint insufficiently strong, and there has been a risk of dislodgment of the neutral-point joint portion occurring if it is subjected to continuous vibration. Thus, another problem has been that stops are required for integrally fastening the neutral-point terminals, increasing the number of work steps and preventing costs from being reduced.
The present invention aims to solve the above problems and an object of the present invention is to provide a stator for an alternator enabling reliability to be improved and costs to be reduced by disposing flat side surface portions on the neutral-point terminals of the strands of wire and constructing the neutral-point joint portions by abutting the side surface portions to each other and electrically joining them so as to eliminate the intricate process of integrating the neutral-point terminals by twisting or using stops and so as to easily ensure a sufficient degree of joint strength.
In order to achieve the above object, according to one aspect of the present invention, there is provided a stator for an alternator, the stator including:
a cylindrical stator core formed circumferentially with a number of slots extending axially; and
a stator winding composed of a three-phase stator winding portion constructed by connecting three winding phase portions into a three-phase star connection, each of the winding phase portions being installed in the stator core by sequentially inserting strands of wire into the slots at predetermined intervals and a neutral point of the stator winding being electrically connected to a rectifier for rectifying alternating-current output, wherein
each of the strands of wire constituting the three winding phase portions is led out from a coil end group of the stator winding to an outer side to constitute a neutral-point terminal,
each of the neutral-point terminals havs a flat side surface portion, and
a neutral-point joint portion of the stator winding is constructed by abutting and electrically joining the flat side surface portions of the neutral-point terminal.
The strands of wire may be conducting wires having a rectangular cross section.
The neutral-point terminals of the strands of wire constituting the three winding phase portions may include:
a first neutral-point terminal positioned centrally in a circumferential direction, the first neutral-point terminal being led axially outwards from the coil end group to constitute a neutral-point lead portion connected to the rectifier; and
second and third neutral-point terminals positioned on first and second sides in the circumferential direction, each being led axially outwards from the coil end group, then bent, and led around to the first neutral-point terminal,
wherein the side surface portions at tips of the second and third neutral-point terminals are abutted and electrically joined from the first and second sides in the circumferential direction to the side surface portions of a portion of the first neutral-point terminal led out from the coil end group.
The stator may also include a connecting member composed of a conductor having flat side surface portions, the flat side surface portions of the neutral-point terminals and the connecting member being abutted and electrically joined to each other.
The connecting member may constitute a neutral-point lead portion connected to the rectifier.
At least a part of the neutral-point terminals extending from the coil end group to the outer side may be secured to the coil end group by means of an electrically-insulating resin portion.
The electrical joining may be welding.